Laboratory testing of coupled hydro-mechanical processes during rock deformation

This paper gives an overview of the published literature on laboratory testing of the stress dependence of rock-permeability. Additionally results of personal research on the stress dependence of the permeability of a low-porosity sandstone are presented. Stress-dependent permeability is examined in the laboratory under different stress fields and stress paths, depending on the intended application of the research. The most commonly applied stress paths are hydrostatic compression, triaxial compression, uniaxial strain conditions, and testing under a constant stress path. The published results of several studies on different rock types under one or more of the mentioned stress conditions are described and compared. A general trend of permeability evolution under hydrostatic and triaxial conditions can be established for sandstones and some crystalline rocks such as granite or rocksalt. For uniaxial strain tests and stress path tests the published results are limited to a few rock types (mainly sandstones). Therefore, a general conclusion for the stress dependence of permeability under these conditions is not possible.